Ovarian biochemical changes associated with chronological aging, with emphasis on steroidogenesis and steroidogenic enzymes, will be sought as signals of physiological change. Plasma steroid levels will be assessed as well as the ovarian response to gonadotrophin. Declining fecundity in aging Long-Evans strain rats will be examined for serum steroid levels. Response to exogenous steroids in intact and ovariectomized older rats will relate to pregnancy maintenance and to placenta growth. The influence of modest hormonal imbalances induced during the neonatal period as potential inducers of premature physiological aging will be evaluated.